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Do Medical Masks Match N95s for COVID Protection in Healthcare Settings?

In a randomized trial, medical masks for preventing infection in healthcare workers interacting with COVID-19 patients fell within predefined margins of noninferiority versus N95 respirators, but researchers warned against drawing firm conclusions due to a host of limitations.

The study involved over 1,000 healthcare workers in four nations, and spanned multiple COVID-19 waves during periods before and well after the rollout of vaccines, ultimately showing a similar 10.5% rate of infection for healthcare workers assigned to medical masks for 10 weeks and 9.3% for those assigned to N95s (HR 1.14, 95% CI 0.77-1.69), reported researchers led by Mark Loeb, MD, of McMaster University in Hamilton, Ontario.

“Although the upper limit of the CIs of the pooled estimate for medical masks when compared with N95 respirators for preventing RT-PCR-confirmed COVID-19 was within the noninferiority margin of 2, this margin was wide, and firm conclusions about noninferiority may not be applicable given the between-country heterogeneity,” the group wrote in Annals of Internal Medicine. “The observed results are consistent with a range of protection, from a 23% reduction in the HR with medical masks to a 69% risk increase.”

Subgroup analyses showed large differences in infection rates, along with variance in the relative protection of medical masks versus N95s, respectively:

  • Canada: 6.1% vs 2.2% (HR 2.83, 95% CI 0.75-10.72)
  • Egypt: 13.6% vs 14.6% (HR 0.95, 95% CI 0.60-1.50)
  • Israel: 35.3% vs 23.5% (HR 1.54, 95% CI 0.43-5.49)
  • Pakistan: 3.3% vs 2.1% (HR 1.50, 95% CI 0.25-8.98)

The high rate of infection in Israel, for example, was attributed to conduct of the study in long-term care facilities with substantial COVID-19 outbreaks. Other large differences between nations included baseline seropositivity, which ranged from 2% in Canada, where enrollment occurred early in the pandemic, to over 80% in Egypt and Pakistan.

“It is notable that there was a close to null effect of medical masks compared with N95 respirators in Egypt, where Omicron was circulating, and from where over half of our participants were enrolled,” Loeb and co-authors wrote.

“It is possible that a higher rate of community transmission could have obscured a higher rate of infection with the medical mask versus the N95 respirator in contrast to what was seen in Canada,” they added.

The multicenter trial is the best evidence to date on masking effectiveness among healthcare workers providing routine patient care, however, “the results are not definitive,” said Roger Chou, MD, of Oregon Health & Science University in Portland, writing in an accompanying editorial.

“The results indicate that medical masks may be similar to N95 respirators in Omicron-era settings with high COVID-19 seroprevalence,” Chou noted.

He pointed to the “generous” noninferiority threshold, which allowed for a 5% absolute increase in COVID-19 incidence with medical masks. This potential doubling of risk “may be unacceptable to many health workers,” he wrote.

Furthermore, the trial did not compare outcomes based on vaccination status and was “unable to assess the effect of Omicron or other variants on mask effectiveness,” he added.

“Decisions about mask types in healthcare workers should be informed by the uncertainty around the estimates and continue to account for healthcare worker preferences about potential tradeoffs, N95 respirator availability, and resource constraints,” Chou concluded.

The randomized study took place from May 2020 to March 2022. In all, 1,009 participants who provided direct care to patients with suspected or confirmed COVID-19 in specialized COVID-19 units, pediatric units, and long-term care were randomly assigned 1:1 to medical mask or N95.

The trial was initially launched in Canada (n=266), but sites in Egypt (n= 518), Pakistan (n=186), and Israel (n=34) were added to increase enrollment. Most of the COVID-19 variant exposure was pre-Omicron, except for Egypt, where enrollment begin in December 2021.

Researchers said baseline characteristics were balanced overall, and the exposure to patients with confirmed or suspected COVID-19, minutes of exposure, and community exposures were similar between study groups.

Weekly self-reported adherence to masking varied, with pooled analyses showing 91.2% of the medical-mask group “always” masking versus 80.7% of the N95 group.

Participants were either unvaccinated or had received a COVID-19 vaccine with lower than 50% efficacy against the current circulating strain. Those who had one or more high-risk comorbidities for COVID-19 were excluded.

  • Ingrid Hein is a staff writer for MedPage Today covering infectious disease. She has been a medical reporter for more than a decade. Follow

Disclosures

The study was funded by the Canadian Institutes of Health Research (CIHR), the World Health Organization (WHO), and Juravinski Research Institute.

Loeb disclosed relationships with CanSino Biologics, Medicago, Pfizer, and Sanofi. Co-authors reported grants or funding from, or other relationships with AMAG Pharmaceuticals, Bayer, the Bristol Myers Squibb-Pfizer Alliance, CIHR, LEO Pharma, the Academy of Continued Advancement in Healthcare Education, Thrombosis Canada, the Ontario Hospital Association, Ministry of the Attorney General of Ontario, the Royal College of Physicians and Surgeons of Canada, Pfizer, Seneca College, Servier, Valeo, WHO, and several other medical societies.

Chou disclosed a relationship with the WHO.

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Source: MedicalNewsToday.com